The present invention relates generally to hermetic compressors for use in cooling, refrigeration or air-conditioning systems, and more particularly to hermetic scroll compressors.
Well known to those having skill in the art are hermetic scroll compressors such as compressor 10 of FIG. 1, having a closed hermetic housing 12 comprised of cylindrical section 14 with end cap 16 welded at the upper end thereof and base 18 at the lower end thereof. Base 18 includes a plurality of mounting feet 20. Compressor 10 has electric motor 22, which comprises stator 24 fixed inside cylindrical section 14 by, for example, shrink-fitting. Surrounded by stator 24 is rotor 26, which is attached to shaft 28 by, for example, press-fit. Counterweight 27 is attached to an upper end of shaft 28 and counterweight 31 is attached to rotor 26, as is customary, to provide substantially balanced rotation of shaft 28. Shaft 28 is coupled to orbiting scroll 30 through eccentric 29. Shaft 28 is supported, at opposing ends thereof, by bushing 32 and auxiliary bearing 34. Bushing 32 is fixed within main bearing 48 by, for example, press-fit. Main bearing 48 and auxiliary bearing 34 are rigidly affixed to an internal surface 33 of cylindrical section 14 of housing 12 typically by press-fit or spot weld methods. Generally, auxiliary bearing 34 includes a plurality of outwardly extended legs 36 secured to internal surface 33 of cylindrical section 14.
Those having skill in the art of compressor construction readily appreciate that spot welding, although a preferable manufacturing process to attach the bearings to the housing, may cause heat generated distortion which can lead to misalignment of stator-rotor air gap 38. To facilitate this process, radially directed holes 40 are provided in an end portion of each leg 36 to accommodate a steel pin 42 in each hole. This process further requires each pin 42 to be aligned with each corresponding hole 44 provided in a lower part of cylindrical section 14. Finally, each pin 42 is spot welded to cylindrical housing section 14 at hole 44.
Turning now to the construction of the scroll compressor mechanism 57, in the upper part of housing 12, is non-orbiting scroll member 46 axially fixed to main bearing 48 by a plurality of bolts 50 in such a manner that orbiting wrap 52, integral with orbiting scroll member 30, and non-orbiting wrap 54, integral with non-orbiting scroll member 46, combine to form compression cavities or chambers 56. Orbiting scroll member 30, non-orbiting scroll member 46 and main bearing 48 comprise compressor mechanism 57 which is positioned in an upper part of cylindrical housing section 14. A typical procedure associated with assembly of compressor 10 includes request for concentricity of inner radial surface 59 of stator 24 respective of inner radial surface 61 of main bearing 48. Annular bushing 32 attached to main bearing 48, by typical means such as press-fit, is substantially concentric with main bearing 48. Main bearing 48 and bushing 32 must also properly align shaft 28 to provide suitable clearance between orbiting and non-orbiting wraps 52 and 54, respectively, so proper compression in compression chambers 56 may be attained. After alignment is achieved, main bearing 48 and/or non-orbiting scroll member 46 is welded to housing 12.
Discharge gas compressed by compressor mechanism 57 flows through discharge port 64 provided with check valve 62, and into first discharge chamber 66. First discharge chamber 66 is defined in part by a volume formed between planar surface 68 of non-orbiting scroll 46 and end cap 16. Thereafter, the discharge gas flows from first discharge chamber 66 to second discharge chamber 70 and exits through discharge tube 72. Discharge chamber 70 is defined by axial surface 78 of compressor mechanism 57, internal surface 33 of a portion of housing 14, generally below compressor mechanism 57, and external surface 55 of the compressor motor 22. Discharge chambers 66 and 70 are in fluid communication through narrow (e.g., 0.035"-0.040"wide) passage 74 formed by internal surface 33 of cylindrical section 14 and peripheral surface 69 of compressor mechanism 57. Discharge tube 72 extends through the wall of cylindrical section 14 of housing 12 and into chamber 70 to transfer refrigerant gas away from compressor assembly 10.
A problem associated with scroll compressors heretofore, is one of excessive noise caused by refrigerant gas turbulently flowing over the compressor mechanism prior to being discharged from the compressor housing. Compressed refrigerant gas exiting discharge port 64 enters first discharge chamber 66, and is thereafter forced over peripheral surface 69 of compressor mechanism 57 and into second discharge chamber 70. Narrow passage 74, disposed between first discharge chamber 66 and second discharge chamber 70, is substantially flow-restrictive and consists of a thin ring or annular shaped passage between cylindrical section 14 of housing 12 and compressor mechanism 57. An outer profile of compressor mechanism 57, exposed to the refrigerant gas flowing thereover, is generally cylindrical, and includes a pair of axially opposed and generally planar surfaces 76, 78, respectively, which are connected by cylindrical surface 80. The transition of discharge gas flow from axial planar surfaces 76, 78, respectively to cylindrical surface 80 generally includes moderately sharp edges which generate turbulence when refrigerant gas flows over compressor mechanism 57. An increase in noise is attributable to an increase in energy of the gas as gas molecules transition from a substantially ordered state to a substantially unorganized and chaotic state. The noise is transmitted through housing 12 of compressor assembly 10 and into the surrounding area.
Another problem associated with compressor assembly 10 arises during operation wherein localized heating occurs between the rotating rotor 26 and the stationary stator 24. Region 25, positioned extending radially through outer peripheral margins of rotor 26 and inner peripheral margins of stator 24, becomes heated which detrimentally affects motor efficiency.
Yet another problem associated with scroll compressors heretofore, is the costly and laborious procedure of aligning the main bearing, auxiliary bearing and stator within the housing to preserve proper scroll wrap and shaft bearing clearances; typically the clearances required are a few ten thousandths of an inch. This procedure is often referred to as "mounting" the compressor.
Mounting of scroll compressors typically requires the diameter of the cylindrical part of the housing to be machined to provide a reference location to concentrically align the main bearing with the auxiliary bearing and to eliminate uneven stator-rotor gap during assembly. Aligning each bearing relative to the housing requires the bearing support structures to include an outer diameter smaller than that of the inner diameter of the cylindrical section of the housing so that a gap is formed between the structure and the inner surface of the housing. The gap must be uniform and somewhat small to facilitate favorable conditions for alignment and spot welding. Further, as mentioned above, typical scroll compressor design mandates precise radial placement of each bearing, thus, a typical scroll compressor exhibits a supporting bearing structure larger than necessary and/or a plurality of special arms attached to the bearing support to allow for radial adjustability. Unfortunately, these design requirements add to the weight of the compressor, complicate assembly and further add to machining time, which in turn, increases the per unit cost to the manufacturer.
Once the bearings and scroll are suitably aligned, the problem of weldability between metals of dissimilar thicknesses and materials must be addressed. For example, welding the relatively thin compressor housing material to the thick bearing support structures often leads to improper joining and/or distortion. Further, often the bearing structures are steel castings, as is the compressor mechanism, while the housing may be formed from cold rolled steel. Those having skill in the art of welding will appreciate that joining by welding depends upon many correlating factors, such as the shape and size of the weld area, material preheat conditions and the speed at which the joined components heat and cool. Distortion of components leads to a complete loss of all materials and labor to that point, often referred to as "scrap", and may be caused by excessive stresses in joined components due to unequal cooling or heating during the welding process. Such undesirable distortion not only resides at the weld location, it also migrates throughout the compressor affecting, for example, precision tolerances such as the bearing gaps, wrap clearances, and the stator-rotor gap.
Therefore, a compressor design which preserves the dimensional tolerances necessary for proper operation of the scroll compressor, which are extremely close, generally on the order of a few ten thousandths of an inch, is highly desirable. Additionally, a design which addresses the difficulties associated with unwanted distortion and stressing of the main bearing, bearing structure, compression mechanism and auxiliary bearing caused by press-fit, shrink-fit and welding is most desirable.
Further, an invention which addresses operational noise, due to discharge gas turbulence internal to the housing, by decreasing the noise without adding significant complexity and cost to the compressor assembly, is highly desirable.